There will be blood: For female jumping spiders, fighting is a life-or-death sport

If you thought watching extreme fighting was a beer-soaked, male-dominated pastime, think again. For behavioral ecologists, brawls between rival animals aren’t just an adrenaline fix – they also shed light on how animals interact.

Not long ago, UC Berkeley professor Damian Elias was part of a research crew that found distinct gender differences in the fighting styles of Phidippus clarus jumping spiders. For male jumping spiders, fighting is a safe way of finding a mate. Between females, fighting is often a matter of life and death. KALW’s S. Howard Bransford tells us more.

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S. HOWARD BRANSFORD: Country music songs, soap operas, reality T.V. shows – they’re all lousy with stories of home wreckers, those femmes fatales that steal lovers and spouses. But in the arachnid world, they’re a lot more than a clich�. Among the Phidippus clarus jumping spiders found in fields throughout North America, home wreckers are a lethal threat.

DAMIAN ELIAS: And they just start – almost instantly – biting each other, wrestling around.

UC Berkeley biologist Damian Elias grew up playing with spiders in his hometown of Nogales, Arizona. Now he studies them for a living.

Recently, Elias took part in a study on the fighting styles of Phidippus clarus jumping spiders. Using tiny cameras, his research team spent months watching spider smackdowns, looking for differences in how male and female spiders settle their differences. With the guys, a distinct pattern emerged.

ELIAS: Males find females that are in their nests, ready to reproductively mature, and they’ll spin a web right next to the female and essentially defend that female against any intruding males, so when the female finally matures, he’ll have sort of first shot at the female and will mate with her.

In other words, fights are mainly a social routine, not too different from what you might see in a dive bar on a weekend night.

ELIAS: They sort of dance back and forth vibrating at each other and waving their legs, and at some point they come together if they decide to and then they start to physically fight, where they push each other, and then usually one wins, and then the other one sort of does this victory symbol where they vibrate continuously at the other male, essentially saying to stay away, and establishing his role as the victor.

So what are those vibrations he’s talking about? They’re fight songs the spiders make by shaking their abdomens. Humans can’t hear them, but Elias recorded them with a laser vibrometer, a device that turns vibrations into sound.

ELIAS: There’s no direct fighting at this point, so it’s mainly a lot of signaling. It’s mainly a lot of, ‘I have this…’ They’re signaling their motivation and their size.

What’s it like when female jumping spiders get ready to rumble? Unlike males, who fight for sex, females fight for a safe place to lay eggs. In a jumping spider’s life, the period of time for having children is quite short, and finding a suitable nest is crucial. That makes fighting off a home wrecker a lethal game.

ELIAS: Sperm is cheap, eggs are expensive. If you imagine a male, it’s really good to win, because they get to mate with a female. It’s not that big of a deal to lose because then a male can just sort of move on and fight again, and hope he finds an opponent that’s smaller or weaker. Now for females, the cost of them losing a fight, and losing the opportunity to mature in safety or to lay eggs in safety, is much, much higher than winning.

When females fight, there’s no song, no dance. Just ruthless, cold-blooded arachnid anarchy. When Elias pumps the volume of his speakers, it sounds as bad as any ultimate fighting challenge.

ELIAS: So it’s much more vicious, and as one retreats the other one does not let it go, and it’s just a continuous, all out fight with biting, and bleeding. And they’re awful, awful things.

So what can humans gain from this research? Damian Elias says one takeaway is insight into how scarce housing isn’t just a human issue.

ELIAS: Today, there’s a lot of decimation of sort of nature and animal systems, and it’s really important to understand what are the forces that are sort of maintaining animals in the wild, maintaining animals to reproduce in the wild. That’s sort of important to setting up conservation practices.

Keep that in mind next time you’re building a house over a field, or trying to keep your partner from a rival mate. Somewhere, a female jumping spider probably has it rougher than you.

For Crosscurrents, I’m S. Howard Bransford.

Damian Elias’s findings on jumping spiders were published online in the June fourth edition of the journal Behavioral Ecology.